The present invention is directed to an attachment unit made up of a nail and a sleeve displaceably guided on the shank of the nail. The sleeve is axially elongated and has a first section with an abutment flange at one end and an external thread with the flange located at the end of the sleeve spaced furthest from the head of the nail.
Use of a threaded bolt drivable by an explosive powder charge has been found to be particularly economical for the removable attachment of objects to a support or receiving material into which the bolt is driven. Threaded bolts usually include a shank ending in a tip with an axially extending section of the shank having an external thread at a location spaced from the tip. After driving the shank of the bolt into the receiving material, the object provided with a bore for receiving the axially extending section of the bolt with the external thread is placed on and clamped to the receiving material by threading a nut onto the threaded section.
One problem experienced with such threaded bolts is that the tightening moment applied by the nut introduces a tensile force into the bolt and, when there is considerable tightening of the nut, can result in pulling out the bolt.
Such disadvantages do not exist in an attachment member disclosed in the British patent No. 105,560. This known attachment member is formed of a nail and a sleeve to be fixed by means of the nail. The nail has a shank with a head at one end. The sleeve is in the form of a tubular section with an external thread and an abutment flange formed on the section. The abutment flange is located at the end of the sleeve section facing away from the head of the nail. An object to be attached using the attachment member is clamped into contact with the abutment flange by threading a nut on the external thread of the sleeve section.
Adequate tightening of the nut is possible only if the sleeve section is secured against rotation along with the nut. The securing against rotation is particularly dependent on the extent the sleeve is clamped between the head of the nail and the receiving material. The force driving the nail must be selected so that an adequate securement is obtained and, at the same time, the head bearing against the sleeve does not cause deformation of the external thread, since such defomation would interfere with placing the nut on the sleeve. Such an attachment member is unsuitable for use with an explosive powder charge operated device, because of the changing condition in the receiving material the pre-established driving force would result in different depths of penetration of the nail.